Introduction

Direct laser writing is a micromanufacturing technique that employs laser pulses focused on a special light-sensitive resin (photoresist) suitable for initiating two-photon polymerisation reactions to produce, within the volume of the photoresist itself, 3D microstructures of arbitrary complexities and resolutions. The common method of additive manufacturing, thou successful, does not cater for the need of applications that require the printing of degradable scaffolds which can be then removed, adapted, modified, reconfigured, or replaced. An approach often referred to as “subtractive manufacturing”. Thus, there is a need to provide photoresists which make it possible to obtain, by means of 3D microprinting techniques such as, for example, direct laser writing, polymeric architectures that are not irreversible but, on the contrary, are easily degradable, modifiable and adaptable, whilst mechanically reliable and printable with good resolution.

Technical features

The present invention fits into the 3D microprinting sector and relates to a process for producing degradable 3D polymeric nano- or microstructures having sub-micrometre resolution. The process of the invention uses a photoresist formulation comprising a mixture of:

1. Cyclic ketene acetal monomers;
2. Vinyl and/or (meth)acrylic monomers; and
3. At least one photoinitiator.

The process is based on two-photon polymerisation photoinitiated by focusing a laser beam within said photoresist formulation, with the obtainment of polymeric nano- or microstructures degradable under mild conditions and having sub- micrometre resolution.

Possible Applications

• Manufacture nano- and microstructures with architectures of arbitrary complexity and which are characterised by high height/thickness ratios, but at the same time maintain good mechanical properties and stability, and that can be removed in specific conditions.
• Fabrication of degradable masks on 3D objects of use in lithographic processes.
• Fabrication of degradable 3D microstructures for the production of free standing (semi-)metallic membranes.
• Engraving via direct laser writing employing a photo-activated basic system on the printed structure (the formulation act as a positive photoresist)

Advantages

• Polymeric structure obtained can be removed, adapted, modified and reconfigured;
• Improved sacrificial photoresist mechanical stiffness;
• Does not give rise to laser defocusing phenomena due to refractive-index mismatch;
• Allows for controlled degradability of the structures in diverse and orthogonal conditions compatible with other microfabrication methodologies commonly employed.